Hitherto so-called radiation method utilizing silver salt has been applied to obtain a radiation image. On the other hand, a method for imaging a radiation image without the use of the silver salt has been developed. Namely, a method is disclosed in which the radiation penetrated through a subject is absorbed by a phosphor and then the phosphor is excited by a kind of energy so that the energy accumulated in the phosphor is emitted as fluorescence light, and the fluorescence light is detected to form an image.
Concretely, a radiation image conversion method is known in which a panel composed of a support and a stimulable phosphor layer provided on the support is used and one or both of visible light and infrared rays are used (refer to U.S. Pat. No. 3,859,527).
As the radiation image conversion method using stimulable phosphors displaying higher luminance and sensitivity, for example, the radiation image conversion method employing BaFX:Eu2+ type phosphor, in which X is Cl, Br or I, described in Japanese Patent Application Open to Public Inspection, hereinafter referred to as Japanese Patent Application O.P.I. No. 59-75200, the radiation image conversion method employing alkali halide phosphor described in Japanese Patent Application O.P.I. No. 61-72087, and the alkali halide phosphors containing Tl+ and Ce3+, Sm3+, Eu3+, Y3+, Ag+ or Mg2+ as co-activator described in Japanese Patent Application O.P.I. Nos. 61-73786 and 61-73787 are developed.
Further in recent years, a radiation image conversion panel having higher sharpness is required in the field of analysis of diagnostic images. As a means to improve the sharpness, it has been tried to control the shape of the stimulable phosphor itself for improving the sharpness.
As one of such the trials, the method described in Japanese Patent Application O.P.I. No. 61-142497 is employed, in which a stimulable phosphor layer composed of pseudo-columnar block formed by accumulating the stimulable phosphor on a support having fine pattern of unevenness.
Moreover, the following methods have been proposed, the method described in Japanese Patent Application O.P.I. No. 61-142500 using the radiation image conversion panel having the stimulable phosphor layer in which the stimulable phosphor was accumulated on a support having fine patterns to form columnar blocks and cracks between the columnar blocks are developed by a shock treatment; the method described in Japanese Patent Application O.P.I. No. 62-39737 employing a radiation image conversion panel having the stimulable phosphor layer which cracks are formed from the surface side to form a pseudo-columnar structure, and the method described in Japanese Patent Application O.P.I. No. 62-110200 in which a stimulable phosphor layer having cavities is formed by vapor deposition and the cavities are developed by a heat treatment to form cracks.
Furthermore, Japanese Patent Application O.P.I. No. 2-58000 proposes a radiation image conversion panel having a stimulable phosphor layer composed of slender columnar crystal is formed by a gas-phase growing method or a gas-phase accumulation method on a support so that the columnar crystals are formed at a designated angle with the normal line of the support.
Recently, a radiation image conversion panel employing stimulable phosphor principally composed of alkali halide such as CsBr activated by Eu is proposed and high X-ray conversion efficiency, which cannot be obtained by usual methods, can be obtained by the use of Eu as the activator.
The layer formation by a vapor deposition is necessary to form the CsBr:Eu fluorescent layer. In the vapor deposition layer formation, a precision layer thickness distribution can be realized by high accurate arrangement of the substrate and the vapor deposition source considering the physical positions of them.
However, the requirements for improving the luminance and the sharpness are not satisfied by such the radiation image conversion panel having the stimulable phosphor layer formed by the gas-phase growing method, and further improvement has been demanded.
Recently, a high power semi-conductor laser emitting a wavelength of near 680 nm is frequently used as the stimulating energy source since the apparatus can be made compact. However, the transmittance of light of such the wavelength is low in the radiation image conversion panel according to the foregoing techniques, therefore problems is caused in the improvement of the sharpness since the stimulating light tend to be scattered in the stimulable phosphor layer. Moreover, a problem of localization of Eu in the CsBr:Eu caused by scattering of Eu since the thermal diffusion of Eu considerably occurs and the vapor pressure of Eu under vacuum is high. Accordingly, the method of vapor deposition and the material of the substrate are become important with respect to the uniformity of the layer.
The uniformity of adhesion between the substrate and the phosphor layer is important for forming a thick layer of a large area to improve the property of the panel. When a resin exists on the surface of the support, volatile ingredients are evaporated on the occasion of the formation of the phosphor layer so that the vacuum degree is varied and the variation of the layer is resulted since various kinds of solvents and volatile compositions derived from the production process are contained in the resin.